What makes the difference in lubricity of machine oil or grease vs something like olive oil?

Question

Of course stickiness can be a factor, but I’m curious about how the substances differ to make one more slippery than the other?

In: 3

Answer 1

There are 2 main factors that determine how well a certain lubrication works.

1. Viscosity. This is the measure of how well a liquid flows. Typical liquids like water have extremely high viscosity levels while substances like molasses and honey have very low viscosities. All oils/lubes have lower viscosity than water, that way it doesn’t just run off your hand/machine/whatever it is applied to.
2. Hydrophobicity. This deals with how compounds react when exposed to water. The more hydrophobic a compound is, the more it avoids water on contact. This partly explains why some oils are difficult to was away.

Answer 2

There are a couple different factors you need to consider when choosing a lubricant for any application first and foremost is the forces being applied. Next is the viscosity. If the lubricant is too thick then it will actively slow down the machinery you’re trying to lubricate. If it’s too thin then it won’t provide significant enough lubrication. Finally you need to consider operating temperature. Engine oil can handle the high heats of an engine block while olive oil or any other cooking oil would break down into black carbon deposits (like you find in your oven) rapidly under such heat.

There’s also a bunch of additives to most engine oils that help with oil life and protection for corrosion.

Answer 3

First, there are different chemicals that make up the oil. Olive oil will mostly be fatty acids (molecules with an acid group on the end and a long hydrocarbon chain attached to it) while engine oil will contain things derived from crude oil like alkanes, aromatics, polyolefins.

Then there’s a whole bunch of things that go into your engine oil. You get detergents, which make sure solid particles don’t get attached to your surfaces. You have dispersants, which make sure those solid bits don’t form lumps that clog the engine. You have antioxidants which slow down chemical reactions that could break down the oil into something less effective. You have chemical agents that make your lubricant form structures only a few atoms thick to maximise lubricity and fuel economy. You have viscosity modifiers which control how sticky it gets with temperature (oil can be as runny as water if you heat it up enough).

Greases are a weird one as they can actually be tiny particles of solid suspended in a sticky liquid!